A traditionally safe Labour seat, represented for 33 years by George Thomas (who became Speaker in 1976 and was re-elected without party affiliation in 1979). It has returned a Conservative only once, in the Tories' landslide year of 1983, when Stefan Terlezki became the MP.

Cardiff West is entirely within the boundaries of the city of Cardiff, taking up the northwestern quarter of the borough at the boundaries of the boroughs of Rhondda Cynon Taf and Vale of Glamorgan. Population areas within the constituency include Riverside, Pontcanna, St Fagans and Ely. There are some Conservative-voting areas in the north of the seat such as Creigiau and St Fagans, Pentyrch and Radyr, but the bulk of the seat comprises districts towards the centre of Cardiff such as Caerau, Canton, Ely and Riverside which are very strongly Labour.